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A Student Project on Rayleigh-Bénard Convection

Abstract

This paper describes a project where a group of five undergraduate engineering students in the heat transfer course designed, built and tested a portable Rayleigh-Bénard convection apparatus for visualization of the instability patterns that appear in this flow during laminar to turbulent transition. The students had to choose appropriate materials, optimize production cost, determine fabrication techniques for the apparatus, and implement this in the workshop. The students designed the apparatus using SolidWorks TM. Heating of the copper plate was provided by a heating element. The different flow patterns that appear in this flow were visualized by mixing a small amount of Afflair 100 Silver Pearl Pigment in Dow Corning 200 silicon oil. COSMOSFloWorks TM software was used to simulate the instabilities that occurred in the experiments. The constructed device is a valuable learning tool for both present and future engineering students.

Introduction

Rayleigh-Bénard convection and Taylor-Couette flow has been classical cases to study the process of laminar-turbulent transition. The first case occur when a layer of fluid between parallel plates is heated from below while the second flow case appear between two concentric vertical rotating cylinders. In this paper we will describe a student project on Rayleigh-Bénard convection. Many textbooks on introduction to heat transfer includes this fundamental flow case. It is always desirable to have the ability to demonstrate the different topics that are covered in a course. Therefore, it was decided to include the design, fabrication and testing of a Rayleigh- Bénard convection apparatus as a course project.

Bénard1 was the first scientist to experimentally study convection in a fluid layer with a free surface heated from below. Rayleigh2 used linear stability analysis to theoretically explain and study the stability of the fluid motion between horizontal parallel plates with the hotter plate at the bottom. Chandrasekhar3 completed the linear stability analysis of Rayleigh-Bénard convection and Koschmieder4 showed the development of the research in this area during the following couple of decades.

There are only a few experiments including Koschmieder and Pallas5 and Hoard et al.6 that have been able to produce the concentric ring cells in Rayleigh-Bénard convection that according to stability theory should appear with a rigid upper boundary condition.

A group of five undergraduate senior students designed the experimental setup for flow visualizations. The only requirement for the design from the instructor was that the fluid layer would have a specified diameter and that the thickness of the layer could be varied. One student modeled the convection cell using SolidWorks TM while another student completed the bill of materials. A third student concentrated on the COSMOSFloWorks TM simulations after the model was finished in SolidWorks TM. The remaining two students were building the apparatus under

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Matsson, J. (2008, June), A Student Project On Rayleigh Benard Convection Paper presented at 2008 Annual Conference & Exposition, Pittsburgh, Pennsylvania. 10.18260/1-2--3591